Problem: $ E = \left[\begin{array}{rrr}1 & 0 & 0 \\ 1 & 2 & 0 \\ 2 & 2 & 1\end{array}\right]$ What is $ E^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}1 & 0 & 0 \\ -\frac{1}{2} & \frac{1}{2} & 0 \\ -1 & -1 & 1\end{array}\right]$